1. Field of the Invention
The present invention relates to a ceramic electronic component, and more particularly, to a ceramic electronic component having lead terminals in which the lead terminals are bonded to electrodes disposed on a ceramic element.
2. Description of the Related Art
Single sheet type ceramic capacitors (so-called sheet ceramic capacitors), e.g., having electrodes provided on a single sheet (sheet ceramic body) made of a dielectric ceramic, respectively, have a structure in which the electrodes are provided on both of the front and back surfaces of the sheet ceramic body, and lead terminals are bonded to the electrodes via solder.
Conventionally, the electrodes may be baked electrodes formed by applying an electrode paste containing as electroconductive components Ag, Cu, or the like which are metals capable of being easily soldered, and also, or may be plating electrodes formed by a wet plating method.
Moreover, in recent years, investigation has been made of adoption of Ni electrodes, Zn electrode, or the like, which are formed by applying and baking an electrode paste containing a metal such Ni, Zn, or the like as an electroconductive component or by wet plating the metal in which Sn contained in the solder is prevented from diffusing.
With respect to the ceramic capacitors having the structure in which the lead terminals are bonded to the baking electrodes or the wet plating electrodes made of Ag, Cu or the like via solder, when the ceramic capacitors are used in a high temperature environment (e.g., a temperature of about 150xc2x0 C.), Sn contained in the solder used to bond the lead terminals is diffused in the electrodes. As a result, an adhesion force between a ceramic constituting the ceramic element and the electrodes is reduced. This may cause an increase in the dielectric loss of the ceramic capacitor, and may cause the ceramic element to be broken, due to corona-discharging in a void generated between the electrodes and the ceramic, depending on the situation.
Furthermore, regarding the baking electrodes or the wet plating electrodes made of Ni, Zn, or the like, soldering of the lead terminals to the electrodes can not be easily performed. Thus, in some cases, it is necessary to use chlorine-type fluxes, which are questionable from the standpoint of reliability, or to provide another electrode for bonding.
For the purpose of solving the above-described problems, a method (multi-layer structure method) has been proposed, in which an electrode layer to be bonded closely to a ceramic is formed by sputtering, and a soldering layer made of an electrode material having high soldering properties is formed on the electrode layer. Even in the case of a product having electrodes formed by the above-described method, characteristics of the product may be deteriorated when the product is used under a high temperature condition. In fact, the problem with deterioration of the characteristics, caused when used in a high temperature environment, can not be satisfactorily solved.
To overcome the problems described above, preferred embodiments of the present invention provide a ceramic electronic component having lead terminals constructed to be soldered to electrodes easily and securely, having a very high reliability of connection of the lead terminals, and minimized deterioration of characteristics of the component, which may be caused by use in a high temperature environment.
To achieve the above-described advantages, according to a preferred embodiment of the present invention, a ceramic electronic component includes electrodes disposed on the surface of a ceramic element, and lead terminals attached to the electrodes, the electrodes each having a four layer structure including (a) a first electrode layer made of an Nixe2x80x94Ti alloy and constructed so as to be bonded to the surface of a ceramic material of the ceramic element, (b) a second electrode layer made of at least one selected from the group consisting of Cu, Ag, and Au, disposed on the first electrode layer, (c) a third electrode layer made of an Nixe2x80x94Ti alloy, disposed on the second electrode layer, and (d) a fourth electrode layer made of at least one selected from the group consisting of Cu, Ag, and Au, disposed on the third electrode layer, the lead terminals each being bonded to the electrode having the four layer structure preferably via solder.
The lead terminals can be securely bonded to the electrodes, and deterioration of the characteristics of the component when used in a high temperature environment can be prevented by constructing each of the electrodes so as to have a four layer structure including the first electrode made of an Nixe2x80x94Ti alloy and arranged so as to be bonded to the surface of the ceramic material constituting the ceramic element, the second electrode layer made of at least one selected from the group consisting of Cu, Ag, and Au and disposed on the first electrode layer, the third electrode layer made of an Nixe2x80x94Ti alloy and disposed on the second electrode layer, and the fourth electrode layer made of at least one selected from the group consisting of Cu, Ag, and Au and disposed on the third electrode layer, and soldering the lead terminals to the electrode having the four layer structure.
In preferred embodiments of the present invention, as a material for constituting the first electrode layer, an Nixe2x80x94Ti alloy is preferably used because it can achieve an appropriate bonding force for bonding to the ceramic material of the ceramic element. It is presumed that the bonding force between an alloy and a ceramic is a result of bonding between oxygen in the ceramic and the metal (alloy). If the bonding force between the oxygen and the metal is low, the adhesion is insufficient. If the bonding force is excessively high, characteristics of a product will be deteriorated, due to the reduction of the ceramic material. In the case of the Nixe2x80x94Ti alloy used in preferred embodiments of the present invention, a sufficient bonding force can be obtained without deterioration of other characteristics of the product.
The second electrode layer performs a function of securing the conductivity in a high temperature environment and preventing deterioration of the component characteristics. In preferred embodiments of the present invention, as a material for constituting the second electrode layer, at least one selected from the group consisting of Cu, Ag, and Au is preferably used.
The third electrode layer performs a function of preventing diffusion of a solder component from proceeding into the second electrode layer. In preferred embodiments of the present invention, as a material for constituting the third electrode layer, an Nixe2x80x94Ti alloy is preferably used such that diffusion of a solder component is minimized.
The lead terminals are soldered to the fourth electrode layer. In preferred embodiments of the present invention, at least one selected from the group consisting of Cu, Ag, and Au is preferably used as a metal having a high wettability for solder.
That is, in the ceramic electronic component having lead terminals in accordance with preferred embodiments of the present invention:
(1) the first electrode layer has a function of securing appropriate bonding properties for the ceramic material of the ceramic element,
(2) the second electrode layer has a function of securing the conductivity in a high temperature environment,
(3) the third electrode layer has a function of preventing a solder component from diffusing, and
(4) the fourth electrode layer has a function of securing a good wettability for solder, so that the reliability of connection of the lead terminals to the electrodes can be maintained at a high value, and deterioration of characteristics of the component, caused by use in a high temperature environment, can be minimized.
Preferably, the first, second, third, and fourth electrode layers each constituting the electrode are formed by a sputtering method, respectively.
The electrodes having high adhesive properties and soldering properties for the ceramic constituting the ceramic element can be produced easily and securely by forming the first, second, third, and fourth electrode layers each constituting the electrode by a sputtering method, respectively.
However, other methods of forming each of the first, second, third and fourth layers may be used.
Also preferably, the content of Ti of the Nixe2x80x94Ti alloy constituting the first and third electrode layers is in the range of from about 5% to about 20% by weight.
The electrodes having high adhesion and soldering properties for the ceramic element can be formed easily and securely by setting the content of Ti (ratio of Ti) of the Nixe2x80x94Ti alloy constituting the first and third electrode layers to be in the range of from about 5% to about 20% by weight. Thus, preferred embodiments of the present invention are practically effective.
One of the reasons for setting the content of Ti (ratio of Ti) of the Nixe2x80x94Ti alloy to be in the range of about 5% to about 20% by weight is as follows. If the content of Ti is less than about 5% by weight, adhesion of the alloy to the ceramic constituting the ceramic element can not be secured, and moreover, with the ratio of Ni being excessively increased, the Nixe2x80x94Ti alloy is magnetized, so that the magnetron sputtering method can not be applied. Moreover, if the content of Ti exceeds about 20% by weight, the reaction to the ceramic causes heterogeneous phases between the electrodes and the ceramic. This causes the dielectric loss to increase.
The content of Ti of the Nixe2x80x94Ti alloy constituting the first and third electrode layers may be in the range of from about 5% to about 10% by weight.
One of the reasons for setting the content of Ti (ratio of Ti) of the Nixe2x80x94Ti alloy to be in the range of from about 5% to about 10% by weight is as follows. Adhesion of the alloy to a ceramic constituting the ceramic element is excellent, and the increase of the dielectric loss, caused by heterogeneous phases, can be securely prevented.
Also preferably, in the ceramic electronic component having lead terminals, the ceramic element is a sheet ceramic body made of a dielectric ceramic for a single sheet type ceramic capacitor, and the ceramic electronic component is the single sheet type ceramic capacitor.
When preferred embodiments of the present invention are applied to the single sheet type ceramic capacitor having lead terminals in which the ceramic element is a sheet ceramic body made of a dielectric ceramic for the single sheet type ceramic capacitor, a ceramic capacitor having lead terminals achieves high adhesion of the electrodes to the ceramic element, a high soldering strength of the lead terminals to the electrodes, and moreover, excellent stability of the capacitor when used in a high temperature environment.
Other features, characteristics, elements and advantages of the present invention will become more apparent from the detailed description of preferred embodiments thereof with reference to the attached drawings.